Electronic engine control has evolved from mechanical control systems employing simple switches and analog devices to a highly precise fuel and ignition control system employing powerful electronics. The miniaturization and cost reduction of electronics has put the power of the computer age into the hands of automotive engineers. Microprocessors have allowed complex programs involving numerous variables to be used in the control of present day combustion engines, leading to better engine control and performance.
An important facet of combustion engine control is the regulation of air flow into a cylinder by a throttle and accordingly the quantity of fuel delivered into the cylinder. In an internal combustion engine (ICE), a throttle, having a movable throttle plate, directly regulates the power produced by the ICE at any operating condition by regulating the air flow into the ICE. The throttle plate is positioned to increase or decrease air flow into the ICE. The ICE acts as an air pump with the mass flow rate of air entering the engine varying directly with throttle plate angular position or area. Presently, there is a need in the art to precisely control throttle plate position in a throttle body to tightly regulate the flow of air and fuel into a cylinder.
In the operation of a standard vehicle ICE, a driver will depress the accelerator pedal to generate a major portion of a throttle plate position command to vary the throttle plate angle and accordingly the air flow into the ICE. A controller coupled to a fuel injector, monitoring various engine variables, will regulate the fuel that is mixed with the air, such that the injected fuel generally increases in proportion to air flow. If a carburetor is used, the air flow through the carburetor will directly regulate the amount of fuel mixed with the air, with respect to the vacuum or suction formed by the air flow through the throttle body. For any given fuel-air mixture, the power produced by the ICE is directly proportional to the mass flow rate of air into the ICE controlled by the throttle plate position.
The positioning and stability of the throttle plate directly affects the tuning or stability of the ICE. Ideally, when a position command is given to position the throttle plate, the throttle plate will step to that exact position without a large amount of overshoot and undershoot and at a desired angular speed.
When a driver of a vehicle thinks about pushing the accelerator pedal, the intention to accelerate is being communicated from the mind of the driver to the car, through the movement of the foot. The interface between the driver and the vehicle is the accelerator pedal, which takes a finite amount of time to settle into a final position. The accelerator pedal position is translated through a calibration, to the systems that control the throttle plate within the throttle body, to produce the desired amount of torque output from the ICE. This sequence of events culminates in an “acceleration” that the driver desired at the time he/she depressed the accelerator pedal.
In most cases, there exists a physical time delay from control input at the accelerator pedal, which may be described as the initial incremental change in pedal position, to the throttle final position of the throttle plate. The commanded throttle position is typically embedded within the calibration as a two-dimensional look-up table (pedal position and vehicle speed inputs, throttle position output). The driver observes this physical delay as a lag in the vehicle's responsiveness. Although in maintaining certain brand characteristics such a damped response is desirable, in all vehicles certain maneuvers warrant an immediate response by the vehicle (for example, in an aggressive start from a stop and in a passing maneuver from 50 mph to 80 mph). In such driving conditions, the driver consciously demands an immediate response. The time between the initial movements of the pedal, to the final position of the pedal that the driver's foot settles to, is on the order of tenths of a second. This time delay is built into the throttle response lag and is undesirable as perceived by the consumer. This delay is further compounded by the transient response of the engine caused by physical delays such as the inertia of filling air into the intake manifold. The torque generated during a transient response by an ICE is usually less than at equivalent steady state operating points for the ICE.